1. Field of the Invention
This invention relates to a reproduction speed controller for an image signal reproducing apparatus which reproduces video image signal or the like from an information recording medium such as a laser video disk (LVD) or a video tape (VT), and more particularly to a reproduction speed controller capable of reproducing image signal having relatively low frequency without deterioration.
2. Description of the Prior Art
There is known a musical accompaniment playing apparatus which reproduces musical accompaniment from a recording medium such as an Laser Video Disc (LVD) or the like. This apparatus displays images relating to a musical accompaniment and lyrics thereof in synchronism with the musical accompaniment. In the recording medium, images are recorded in the form of a plurality of frame images. One frame image is comprised of two field images, a first field image and a second field image. Each of the field images are displayed for 1/60 sec., and these field images are recognized as a single image by the after-image effect of the eye of the human being.
It is known that some types of musical accompaniment playing apparatuses have a so-called key control function for controlling musical interval, by adjusting a reproduction speed of information part only relating to voice, to be comfortable for a singer who feels difficult to sing a song with an original musical interval (key).
However, the musical accompaniment playing apparatus does not have a function for adjusting the reproduction speed of images displayed in synchronism with the musical accompaniment. In the above apparatus, when the reproduction speed of the image are high, one frame image is omitted from every predetermined number of frame images in accordance with the reproduction speed. On the other hand, when the reproduction speed of the images are low, one frame image is inserted to every predetermined number of frame images in accordance with the reproduction speed. In the former case, there is particularly no problem. In contrast, in the latter case, the following problem occurs.
Namely, if the frame image F.sub.5 is inserted after the same frame image F.sub.5 as shown in FIG. 1, field images are displayed in the order of the ninth field f.sub.9, the tenth field f.sub.10, the ninth field f.sub.9, and the tenth field f.sub.10. Accordingly, when the image shifts from the tenth field f.sub.10 to the ninth field f.sub.9, the order is reversed, which results in a momentary retrogression of images in time. This appears on a picture as a fluctuation of the image. Since such a fluctuation appears every predetermined number of frame images, it is extremely conspicuous.
In order to prevent such inconvenience, it is conceivable to synthesize the field images at a predetermined rate to form a new field image. Further, it is conceivable to use a device which is capable of producing a new frame image from the successive frames such as frame images F.sub.5 and F.sub.6 in FIG. 1. However, such a device is very expensive and, makes the outline of the image unclear.